首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4222篇
  免费   287篇
  国内免费   20篇
耳鼻咽喉   49篇
儿科学   108篇
妇产科学   69篇
基础医学   476篇
口腔科学   40篇
临床医学   468篇
内科学   817篇
皮肤病学   163篇
神经病学   374篇
特种医学   362篇
外科学   578篇
综合类   43篇
现状与发展   1篇
一般理论   4篇
预防医学   366篇
眼科学   55篇
药学   222篇
肿瘤学   334篇
  2023年   27篇
  2022年   53篇
  2021年   154篇
  2020年   87篇
  2019年   108篇
  2018年   114篇
  2017年   104篇
  2016年   91篇
  2015年   102篇
  2014年   126篇
  2013年   161篇
  2012年   248篇
  2011年   257篇
  2010年   132篇
  2009年   112篇
  2008年   226篇
  2007年   221篇
  2006年   210篇
  2005年   211篇
  2004年   172篇
  2003年   182篇
  2002年   171篇
  2001年   98篇
  2000年   72篇
  1999年   78篇
  1998年   40篇
  1997年   41篇
  1996年   34篇
  1995年   30篇
  1994年   29篇
  1992年   45篇
  1991年   56篇
  1990年   35篇
  1989年   41篇
  1988年   43篇
  1987年   29篇
  1986年   24篇
  1985年   44篇
  1984年   44篇
  1983年   31篇
  1982年   22篇
  1980年   22篇
  1979年   48篇
  1978年   28篇
  1977年   22篇
  1974年   30篇
  1973年   35篇
  1972年   19篇
  1971年   19篇
  1970年   19篇
排序方式: 共有4529条查询结果,搜索用时 15 毫秒
1.
ObjectivesCocaine is the second most frequently used illicit drug worldwide (after cannabis), and cocaine use disorder (CUD)-related deaths increased globally by 80% from 1990 to 2013. There is yet to be a regulatory-approved treatment. Emerging preclinical evidence indicates that deep brain stimulation (DBS) of the nucleus accumbens may be a therapeutic option. Prior to expanding the costly investigation of DBS for treatment of CUD, it is important to ensure societal cost-effectiveness.AimsWe conducted a threshold and cost-effectiveness analysis to determine the success rate at which DBS would be equivalent to contingency management (CM), recently identified as the most efficacious therapy for treatments of CUDs.Materials and MethodsQuality of life, efficacy, and safety parameters for CM were obtained from previous literature. Costs were calculated from a societal perspective. Our model predicted the utility benefit based on quality-adjusted life-years (QALYs) and incremental-cost-effectiveness ratio resulting from two treatments on a one-, two-, and five-year timeline.ResultsOn a one-year timeline, DBS would need to impart a success rate (ie, cocaine free) of 70% for it to yield the same utility benefit (0.492 QALYs per year) as CM. At no success rate would DBS be more cost-effective (incremental-cost-effectiveness ratio <$50,000) than CM during the first year. Nevertheless, as DBS costs are front loaded, DBS would need to achieve success rates of 74% and 51% for its cost-effectiveness to exceed that of CM over a two- and five-year period, respectively.ConclusionsWe find DBS would not be cost-effective in the short term (one year) but may be cost-effective in longer timelines. Since DBS holds promise to potentially be a cost-effective treatment for CUDs, future randomized controlled trials should be performed to assess its efficacy.  相似文献   
2.
The safety of epidural anaesthesia in patients with active, recurrent genital herpes simplex (HSV) infections is controversial. We reviewed the six-year experience of the use of epidural anaesthesia in this patient population in two institutions. Eighty-nine parturients with active genital HSV were administered epidural anaesthesia for Caesarean section. No patient suffered an adverse outcome related to either the anaesthetic or the virus. The theoretical risks of regional anaesthesia in the parturient with active herpes genitalis are reviewed. We conclude from available data that the risk of an adverse outcome is small and does not contraindicate the use of epidural anaesthesia in patients with recurrent infection.  相似文献   
3.
4.
The nature of the inputs to achromatic luminance flicker perception was explored psychophysically by measuring middle- (M-) and long-wavelength-sensitive (L-) cone modulation sensitivities, M- and L-cone phase delays, and spectral sensitivities as a function of temporal frequency. Under intense long-wavelength adaptation, the existence of multiple luminance inputs was revealed by substantial frequency-dependent changes in all three types of measure. Fast (f) and slow (s) M-cone input signals of the same polarity (+sM and +fM) sum at low frequencies, but then destructively interfere near 16 Hz because of the delay between them. In contrast, fast and slow L-cone input signals of opposite polarity (−sL and +fL) cancel at low frequencies, but then constructively interfere near 16 Hz. Although these slow, spectrally opponent luminance inputs (+sM and −sL) would usually be characterized as chromatic, and the fast, non-opponent inputs (+fM and +fL) as achromatic, both contribute to flicker photometric nulls without producing visible colour variation. Although its output produces an achromatic percept, the luminance channel has slow, spectrally opponent inputs in addition to the expected non-opponent ones. Consequently, it is not possible in general to silence this channel with pairs of 'equiluminant' alternating stimuli, since stimuli equated for the non-opponent luminance mechanism (+fM and +fL) may still generate spectrally opponent signals (+sM and +sL).  相似文献   
5.
Human multiple sip drinking was simulated by repeated, alternate application of a NaCl solution and a second liquid to the anterior portion of the tongue. Judged intensity of the NaCl solution remained constant during alternation with artificial saliva, increased during alternation with water, and decreased during alternation with an identical NaCl solution or with no second liquid. Relative change in concentration on the tongue may determine constancy, facilitation, or adaptation during drinking.  相似文献   
6.
Background In recent years, the number of women entering the field of emergency medicine (EM) has increased.
Objectives To determine if authorship in EM publications has increased in parallel with this trend.
Methods The gender of first and last authors of EM articles in Academic Emergency Medicine , American Journal of Emergency Medicine , Annals of Emergency Medicine , and Journal of Emergency Medicine were examined. The authors reviewed articles from 1985, 1995, and 2005 for American Journal of Emergency Medicine , Annals of Emergency Medicine , and Journal of Emergency Medicine and from 1999 and 2005 for Academic Emergency Medicine . The primary outcomes were the proportions of female authors.
Results A total of 2,016 articles were reviewed. Overall, 18% of first and last authors were female. Respectively, for 1985, 1995, 1999, and 2005, the proportions of female first authors were 9%, 15%, 19%, and 24%; the proportions of female last authors were 9%, 18%, 19%, and 22%. The trend of increases in female authorship was statistically significant.
Conclusions Although female authorship remains a minority in EM publications, it has increased significantly in parallel with increases in female participation in EM.  相似文献   
7.
We evaluated the relative contribution of plain radiographs and computed tomography to the assessment of fracture healing under experimental circumstances. In 15 sheep, we performed midshaft femoral osteotomies and internal fixation of the resultant segmental fractures. Radiographs were obtained preoperatively and immediately postoperatively. Animals were sacrificed at 3 weeks, 6 weeks, 12 weeks, 24 weeks, and 36 weeks after surgery, and the femoral specimens radiographed. After removal of the internal fixation devices, computed tomographic scans of the specimens were performed.By 3 weeks, callus was visible, but at 6 weeks, a trabecular pattern in the callus was seen on plain films but not on computed tomography. There was progressive organization of the callus on both studies. At 24 weeks, computed tomography demonstrated fracture lines not seen due to overlying callus on plain films and also more accurately showed incomplete union. By 36 weeks, healing was essentially complete according to both modalities, although there still were small gaps in the callus detectable on computed tomography but not on plain films.Computed tomography may be of value in the evaluation of fractures of long bones in those cases in which clinical examination and plain radiographs fail to give adequate information as to the status of healing.  相似文献   
8.
9.
Guanine nucleotide-binding proteins (G proteins) transduce signals from agonist- and light-sensitive receptors. In the visual excitation system, the photon receptor rhodopsin is coupled to the G protein Gt (transducin). Gt is composed of alpha, beta, and gamma subunits; the alpha subunit binds guanine nucleotide, whereas the beta and gamma subunits, which are tightly associated, appear to facilitate interaction of alpha with receptor and pertussis toxin-catalyzed ADP-ribosylation of alpha. To study the function of transducin, monoclonal antibodies were developed against the purified protein. Monoclonal antibody 2H3 reacted with Gt gamma but not G gamma from bovine brain or rabbit liver. In the absence of photolyzed rhodopsin, both intact 2H3 and Fab fragments of 2H3 were able to inhibit completely, in a concentration-dependent manner, ADP-ribosylation of transducin by pertussis toxin 2H3 had no effect on ADP-ribosylation in the presence of photolyzed rhodopsin. The GTPase activity of transducin, which is dependent on rhodopsin, was inhibited only 50% by 2H3. These data are consistent with the hypotheses that an epitope recognized by 2H3 may be important in the formation of the alpha beta gamma complex or that interaction of 2H3 with gamma may alter conformation of the latter and, thereby, inhibit complex formation. Further, reactions of gamma with 2H3 appear to be prevented by interaction with rhodopsin, suggesting that its interaction either shields or alters the epitope recognized by 2H3.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号